The role of bone marrow edema and lymphangiogenesis in inflammatory-erosive arthritis.

A common feature of autoimmune diseases is the perpetual production of macrophage, dendritic and/or osteoclast effector cells, which mediate parenchymal tissue destruction in end organs. In support of this, we have demonstrated previously that patients and mice with inflammatory-erosive arthritis have a marked increase in circulating CD11b+ precursor cells, which are primed for osteoclastogenesis, and that this increase in osteoclast precursors (OCPs) is due to systemically increased TNF production. From these data, we proposed a unifying hypothesis to explain these osteoimmunologic findings during the pathogenesis of inflammatory-erosive arthritis, which has three postulates: (1) myelopoiesis chronically induced by TNF has profound effects on the bone marrow and joint tissues that should be evident from a longitudinal MRI; (2) TNF alters the chemokine/chemokine receptor axis in the bone marrow to stimulate OCP release into the blood, and (3) OCP-mediated lymphangiogenesis occurs in the end organ as a compensatory mechanism to drain the inflammation and remove by-products of joint catabolism. Here, we describe our recent experimental findings that support these hypotheses and speculate on how this information can be used as diagnostic biomarkers and tools to discover novel therapies to treat patients with inflammatory-erosive arthritis.